Pickup storage tube



Dec- 20, 1966 YosHlAKl NAKAYAMA ETAL 3,293,484

PICKUP STORAGE TUBE Filed March 19, 1964 2 Sheets-Sheet l FGJ +100 +1.5V 36M uw l0 @1 i @havia C21-; l2 3 I3 E @1i 6% M ,6M-05V@ 15 I7 .Q

i SL 12 HR-4T AMP 1 Wu/LV; 1MM/ww- 2 Sheets-Shed'l 2 INVENTOR.

DGC- 20, 1966 YosHlAKl NAKAYAMA ETAL.

PICKUP STORAGE TUBE Filed March 19, 1964 United States Patent Q 3,293,484 PICKUP STORAGE TUBE Yoshiaki Nakayama, Ohta-ku, Tokyo, Kaichiro Odagawa, Tsurumi-ku, Yokohama-shi, and Shin Hasegawa, Kamakura-shi, Japan, assignors to Tokyo Shihaura Electric Co. Ltd., Kawasaki-shi, Japan, a corporation V@Japan Y Filed Mar. 19, 1961i, Ser. No. 353,038

3 Claims. (Cl. 315-11) This invention relates to pickup storage tubes by which an optical object can be sho-t, stored as a still or positive electric charge image, and continuously read out for desired hours after desired hours.

There are presently available, pickup tubes in which an image is stored as an electric charge image and reproduced as image signals. For instance, an image orthicon type pickup tube has a face plate at one end of a glass envelope, and on the inner surface of the face plate provides a photocathode, on which an optical image is focused by an optical system which is provided in front of the face plate. The photocathode emits photoelectrons of an amount which corresponds to the image brightness. The photoeleetrons are accelerated by the accelerating electric eld, run along the magnetic line of force which are almost parallel to the glass bulb axis, strike at high speed the target face which is arranged so as to face the photocathode and emit secondary electrons, building up on the target face a positive charge image which `corresponds to the optical image. The emitted secondary electrons are collected by the collector mesh which is provided in front of the target in parallel and adjacent thereto. The target is usually made of a glass membrane which is so thin that the lateral leakage is negligible and that the charge reaches the scanning side of the target in a short time.

The positive charge image transmitted to the back of the target is scanned by scanning electrons emitted from the electron gun which is provided at the other end of the glass envelope. When the scanning electrons approach a particular point on the scanning side of the target, the electrons adhere to the target in proportion to the positive charge at that point. The excess electrons are repelled by the target and return towards the electron gun passing through almost the same route as that of the scanning beam. As the returned beam is modulated in proportion to the charge at the target, the modulated beam is collected into the multiplier, and comes out as output signals after fully multiplied. Those pickup tubes are so designed as to erase with one frame scanning of electron beam a charge image stored `at the target. These pickup tubes are inconvenient to shoot and later observe for a desired time period a momentary sports scene where objects move quickly, or to shoot very dark stars, etc. with long exposure time in astronomical observation, because in these pickup tubes, when incident light is olf, image signals cannot come out; exposure time may be lengthened up to several seconds, but resolution is decreased because of lateral leakage of stored charge of the target. In this case, too, observation is possible only at a moment when the beam is on.

For these observations, the system which is made by combining the pickup tube above mentioned with a storage tube so as to store in the storage tube image signals obtained by the pickup tube and to `read them out repeatedly at desired time is proposed, that is, the above mentioned storage tube has capability to store image signals as charge images and to read them out as image signals again afterwards, and consists of one or more electron guns which emit reading and writing electron beams and of a storage target; both of them are contained in the vacuum envelope. This storage target is made of a mesh with proper neness on the whole surface of which aneinsulator is coated to such an extent as not to stop up the mesh holes, and so arranged that the insulator side is opposite to the electron gun which emits a writing beam. In such a storage tube, the storage target is scanned by a writing beam modulated by image signals, and a charge image is built up on the insulator surface `ot the target. By building up the charge image, the storage target is responsive to mesh control in proportion to charge distribution, and controls the quantity of the emitted reading electron beam which passes through the storage target. Accordingly the reading electron beam is modulated during passing through the storage target, collectedV by the collector mesh which is provided behind the target, and comes out as output signals, which can come out repeatedly.

In such a system by combining .a pickup tube with a storage tube, however, noises of the pickup tube and the storage tube themselves, noise of a signal transmission circuit from the pickup tube to the storage tube, and distortion are accumulated, which causes deterioration of the signal to noise ratio of the nal image.

The principal object of this invention is to obtain a pickup storage tube which has the capability of shooting a momentary scene of an object, storing it and reading it out `repeatedly as image signals for desired period of time.

Another object of this invention is to provide a pickup storage tube in which image signals with good signal to noise ratio can be read out repeatedly as output signals.

Still another object of this invention is to provide a pickup storage tube which can repeatedly read out image signals with high resolution as output signals.

A further object lof this invention is to provide a pickup storage tube in which an image with proper contrast and good signal to noise ratio can be obtained, which is impossible in the conventional storage system.

Other objects and advantages of this invention will be apparent from the following description taken in connection with the accompanying drawings, in which FIG. 1 is a schematic diagram of the tube of this invention illustrating one embodiment thereof;

FIG. Za is an enlarged diagram of a part of the storage tube shown in FIG. 1 to show its performance, FIG. 2b shows an enlarged cross-section of one of the targets shown in FIG. 2a; and

FIGS. 3, 4 and 5 are partial schematic diagrams of the tube of this invention illustrating another embodiment thereof.

Referring now to the accompanying drawings and more particularly to FIG. l, the pickup storage tube of the invention consists of a glass envelope 10, one end of which is an enlarged portion 11. The end face of the enlarged portion 11 is made of a transparent face plate 12, to the inner surface of which adheres a Iphotocathode 13. The photocathode is sensitive to the optical image which is focused through the face plate and emits photoelectrons in proportion to distribution of brightness of the image. A storage target is opposite with some distance to the photocathode, close to the other end of the enlarged portion. Between the photocathode and the storage target is provided a collector cup anode 17 on which a circular accelerating electrode 15 and a collector mesh are mounted en bloc,

While writing the target 14 and each electrode 15 and 17 are applied positive to the photocathode 13, and accelerate to the target 14 4direction photoelectrons emitted on the photocathode A solenoid coil 118, which envelops whole length of the glass envelope 10, is prepared, and by the coil supplied with direct current it gives a magnetic eld which has magnetic line of force along the tube axis. Therefore, photoelectrons travel along the magnetic line of force and strike the target. As shown in FIG. 2a, this target has a mesh 20 with proper fineness, for instance, 750 to 1000 meshes/inch, which is made of metals such as copper and nickel. v Such insulators as calcium fluoride, magnesium fluoride and silicon dioxide are deposited on one face of the mesh which is lfacing to the photocathode, in such an extent as not to stop up the mesh holes. The coating is done by vacuum deposition, spray, and settling, all of which are well known. And then on the other face, such conductive materials 22 as gold, silver and aluminum aire thinly evaporated which improves control characteristics of the storage target.

The photoelectrons arrived at the target 14 strike the surface of the insulator 21 and emit secondary electrons, which are collected by the collector mesh 16 prepared near the target 14. By the emission of the secondary electrons, a positive charge image which is analogous to the optical image is focused on the insulator surf-ace of the target.

In the invention the above mentioned performance corresponds to the writing in an ordinary storage tube; for instance, when potential of an electron gun cathode, which will be described later, is volt, potential of each electrode is: photocathode -13:; -430 v., .accelerating electrode 17; -290 v., collector mesh 16; +10 v., storage target 14; -1.0 v. as shown in FIG. 1. This is of course one example of operation, and the invention is not limited to this.

At the opposite side of the enlarged portion in the glass envelope 10, an electron gun 24 is prepared which comprises a cathode Z and a grid electrode 26, and emits electron beams. Sharp electron beam emitted from the electron gun 24 is aligned in the same direction as that of the tube axis by the alignment magnetic eld produced by an alignment coil 27 which is arranged out of the `glass envelope 10. In the tube, a magnetic field exists which is produced by a focusing coil 18 and has magnetic lines almost parallel to the tube axis; electron beam runs along the magnetic line of force. A deecting coil 28 is prepared out of the .glass envelope 10 only at the part where the beam passes through, and the deflecting coil supplied with currents produces a deflecting magnetic field. The tar-get 14 is scanned by deflecting the beam horizontally and vertically. Between the electron gun 24 and the target 14, a multiplier focus electrode 29, a focus electrode 30 which is made by evaporating such conductive material as aluminum on the wall of glass envelope 13, and decelerating electrode 31 are arranged in this order from the electron gun side, and voltage is applied so as to generate a decelerating electric iield to the electron beam. Accordingly the electron beam is decelerated and reduced to almost 0 volt in the the same path as that of the scanning beam. A secondary electron beam multiplier 32 is set around ther electron gun, and lthe repelled beam is persuaded by the multiplier focus electrode 29 into the multiplier Where the repelled beam is collected and multiplied. The

multiplied beam current is taken out of the tube, and

causes voltage drop in resistance 33. The voltage drop is led as output signals to preamplier 35 through a coupling condenser 34. The reference numeral 19 designates a direct current source to .apply voltage to each electrode in t-he tube.

The construction of -the tube of this invention has lbeen briefly described above 4with respect to its main oper-ation. The operation of the tube constructed in accordance with this invention will now be described in detail.

The pickup storage tube of this invention can be operated in two different modes. The one is to read out signals after a certain exposure time and the other is to read out signals during exposure.

T-he lformer Iwill be described rst.

a. Shooting (wrting).-An object is focused on the photocathode 13 by Ian optical lens (not sh-own). Photoelectrons emitted from the photocathode are accelerated by an accelerating electrode eld formed by means of collector cup anode 17 and circular accelerating electrode 15 at about 500 volts. 'Ihe electrons travel along magnetic lines of force which is produced by the focusing coil 18 and substantially in parallel with the tube axis; and out of these photoelectrons those which can pass lthroulgh the collector mesh 16 strike and focus on the surface of insulator 21 of target 14, Iand emit secondary electrons from the insulator surface. Thus, a positive charge image which agrees to brightness of the optical image is built up on the storage target. Potential at light part is for instance +3 volts, and that at dark part 0 volt. In this case, it would be better to cut off the electron beam.

b. Reading-Reading a stored charge image will be described. In the case of emitting electron beam from the electron gun 24 and making them scan the storage target 14, the potential of the insulator surface controls the transmission of the electron beam, that is beam 36 with a large number of electrons passes through a low potential part, as shown in FIG. 2a. Accordingly surplus electron beam 37 is repelled beam has already been modulated by the stored charge and come out as large multiplied signals from the secondary electron beam multiplier 32. 'Ihe electron beam that passes through the target is collected by the collector mesh 16 or the photocathode 13. (Note that potential must be positive while reading.) As this electron beam little destroys stored charge, it is possible to read continuously a stored image more than 30 minutes, which corresponds to about 100,000 frame scanning in the standard television system with 30 fname scanning/sec. It must be noted in this case that potential .at the photocathode is desirable to be kept positive, because if the photocathode is kept negative same as at shooting, electrons which have passed the collector mesh return to the storage target again and accelerate destruction of stored charge.

c. Erasing-Erasing is done by light ash on the Whole photocathode by keeping potential at the same arrangement as at writing. Thus positive charge is stored on the insulator surface of the target, that is, on the whole part of the storing face, and the stored charge image is erased.

Erasing can Ibe effected by electron beams instead of using a light flash. In this operation, for instance, the scanning beam is emitted in the condition that the collector mesh 16 potential is -3 volts and the storage mesh 20 potential is +150 volts. The beam which passes through the storage mesh is repelled just before the collector mesh strikes the insulator 21 surface, and makes potential of the insulator surface uniform by emitting the secondary electrons.

d. Prmzng for writing- Potential of the insulator surface after erasing is not necessarily desirable potential for writing. So priming is necessary to make proper the potential between the storage mesh 20 and the inSulator 21 surface. In this case, for example, the collector mesh 16 is kept at 3.0 volts and the storage mesh Z0 is at 1.0 volt. The scanning beam is emitted about 3 seconds, and then the potential of the insulator surface is brought to zero volt and priming is finished.

In each operation mentioned above, one example of the 6 Image signals for a reproduced picture with a better signal to noise ratio can be obtained, compared with the conventional system of combining a pickup tube with a storage tube. This is because of that photelectrons are potential applied to each electrode is shown in the fol- 5 directly stored in the storage target and little noise is lowing table. It should be noted that the potential of added in the reading system by the pickup storage tube. the electron gun cathode 2S is zero volt. FIG. 3 shows another example of application of the tube Voltage (V.)

Photo- Accelerating Collector Storage Deceler- Focusing Multiplier Operation cathode electrode mesh mesh ating electrode focusing Incident light 13 (15) electrode electrode electrode (30) electrode 430 200 +100 -1.0 +130 +280 +2s5 Uniform. 430 -290 0 -1 0 +130 +280 +235 o +430 +200 +10 1.0 +130 V+230 +285 optical object. +350 +230 +100 -1.5 +130 +280 +285 otr.

The second mode of the operation, that is, reading during writing will be described.

In this operation, the way of applying the working voltage is same as that mentioned in the paragraph 11. Writing of the first mode. But in this case the scanning beam current is on and the collector mesh voltage is decreased to, for instance, as low as 2 volts. If a light is off, a stored image is erased in a few seconds; if the incident light is adjusted to proper value an image with good signal to noise ratio is obtained for a stationary object. When the object is charged, the old signal decays gradually in a few seconds, and at the same time the new signal is built up clearly. In the second mode of operation, it is not necessary to erase the old signal one by one nor to shoot afresh; it is convenient for adjusting optical focus, though it is not suitable for the object with too quick movement. An image with good signal to noise ratio and good contrast can be obtained for the dark object, because the effective exposure time is long in this case.

ln such an operation, one example of the potential to be applied to each electrode is shown in the following table wherein the potential of the electron gun cathode of this invention. The construction of the tube is same as that shown in FIG. 1 and the same reference numerals are intended to designate the same parts in the both figures. In this embodiment, signals come out not by the repelled beam but -by the beam passing through the storage target 14, differing from the example shown in FIG. l, i.e., the electron beam which scans the target during reading is controlled in the quantity passing through the target, according -to charge distribution stored on the insulator surface of the target. Accordingly, the beam has been modulated and when it is collected by the collector mesh 16, the signal current is taken out of the tube through the collector mesh, which causes fall of potential of the resistance 40. The output signals are led to the preamplifier 42 through he coupling condenser and modulated positively. The output signals come out by the use of the photocathode 13 instead of the collector mesh 16. This mode of operation does not necessitate the secondary electron multiplier but can be applied to the system with the multiplier.

FIG. 4 shows the other embodiment of this invention. The electron beam scanning part containing the electron gun and others will be omitted, because the construction is zero volt. is the same as the embodiment shown in FIG. 1. The

Voltage (V.)

Photo- Accelerating Collector Storage Deceler- Focusing Multiplier Operation cathode electrode mesh mesh ating electrode focusing Incident light electrode electrode electrode (30) electrode Write and Read -430 -290 +2 -1.5 +130 +280 +285 Optical object' The practical examples have been described, and the pickup storage tube relating to this invention has the following advantages.

The stored image, after shooting a momentary optical image, can continuously be observed for desired period of time and moreover not so much a degraded image can be observed even after 15 hours, if the stored image is not read continuously after shooting. The dark object, for instance, or star which cannot be observed by a conventional pickup tube can be observed by making exposure time longer in the tube relating to this intention.

As to a stationary object, in the case that the contrast of the reproduced image is found to be poor when it is observed after a certain period of time of exposure, the image with suitable contrast can be obtained by additional exposing to integrate more electric charge images than the afore exposing.

The exposure 4time can be determined independently of the television system and improvement of the signal to noise ratio is possible by integration of positive electric charge on the storage target which is caused by long exposure time. It was proved by application to an X-ray television and a betatron television.

same reference numerals designate the same parts in FIGS. l-and 4.

The one end of the swelling part 11 of the glass envelope 10 consists of the face plate 12, the inside of which has the photocathode 13 and the other end the swelling part has the storage target 14. Between these electrodes 13 and 14 are provided a first accelerating electrode 43, a second accelerating electrode 44, an intensifying target 45, a third accelerating electrode 46 and a collector mesh electrode in the order described from the photocathode side 13. The intensifying target 45 has the capacity to convert an electron image into an optical image and then into a much intensified electron image, and consists of the transparent basic plane 47, on the photocathode side 13 of which is evaporated a iluorescent layer 48 and on the other side face of which is provided another photocathode 49. On the upper part of the fiuorescent membrane 48 may be formed a metal thin film S0 of aluminum and others so as to prevent the fluorescence of the iiuourescent layer 48 from lighting the photocathode layer 13. The transparent basic plane 47 is desirable to work as a fiber optics plane to prevent the light of the basic plane from scattering.

When an optical image is focused on the photocathode 13 by an optical system (not shown), photoelectrons are generated according to the brightness of the image. The photoelectrons are accelerated by the accelerating electrodes 43 and 44, travel along the magnetic line of force substantially parallel to the tube .,axis, and strike the fluorescent membrane 48 to emit light. The obtained fluorescent image in a similar one to an optical image and excites another photocathode 49 through the transparent plate 47.

Consequently, intensified photoelectrons are emitted from the photocathode and strike the storage target 14 accelerated in the accelerating electric field generated by the third accelerating cathode 46 and the collector mesh 16. Thus, on the surface of insulator 21 of the target is formed a positive charge image. The successive reading operation is the same as that shown in FIG. 1, which will be self-explanatory. In addition, electrostatic focusing of photoelectrons is possi-ble.

The tube in this case has extremely high sensitivity as a result of the arrangement of the intensifying target 45 and is quite effective for instantaneous photographing of the moving objects and the observation of dark objects as in astronomical observations.

In the example shown in FIG. 5, the glass envelope contains fluorescent membrane 51 which is induced to radiate lby X-rays and the photocathode which emits photoelectrons in proportion to the radiation.

When an X-ray image is focused, a fluorescent image is emitted from the fluorescent membrane 51, which excites the photocathode 13. Simultaneously, the photocathode 13 emits photoelectrons in accordance with the brightness of the fluorescent image.y The photoelectrons are electrostatically accelerated and focused by the electric field by the focusing electrode and the collector mesh electrode, and strike the storage target 14. Consequently, on the insulator 21 surface of -the target is built up a charge image, reproduction of the X-ray image. The reading out of the charge image which is the same ,as in FIG. 1 will be self-explanatory.

In this example, the electrostatic accelerating focusing of photoelectrons is done, but it goes without saying that electromagnetic means is applicable. The same reference numerals designate the same part in -both FIGS. 1 and 2. l

In an ordinary system combining an optical lens and an X-ray brightness intensifier tube with a pickup tube, images cannot be obtained Without continuous X-ray irradiation. This causes the large quanta of X-ray dose and is destructive to human body.

When this embodiment is used, an excellent reproduced image can be observed for more than minutes only by momentary X-ray irradiation.

In an ordinary system stated above, the pickup tube can produce only a noisy picture while this embodiment produces an image with far lbetter S/N, as the signal is stored in the storage target.

1. A pickup storage tube adapted for storing an optical image as a charge image for a desired period of time comprising a vacuum envelope having a face plate at one end thereof,

a photocathode deposited on the inside of said face plate and adapted to emit photoelectrons in accordance with the brightness of the optical image focused on said photocathode,

a storage target spacedly positioned from said photocathode oppositely from said face plate,

said storage target including a metallic storage mesh having openings therethrough,

an insulator coating on said mesh on the side facing sai-d photocathode whereby secondary electrons are emitted after said insulator coating is struck by said photoelectrons and charge images are stored on the surface of said insulator coating,

and a conductive material coating on said mesh on the opposite side from said insulator coating,

a collector mesh electrode located adjacent and parallel to said target on the side with said photocathode adapted to collect emitted secondary electrons,

an electron gun provided at one end of said envelope opposite from said photocathode and adapted t0 emit a reading electron beam,

said reading electron lbeam scanning said target,

and means to collect electrons moving from said target through the action of said reading electron beam whereby the optical image may be stored as a charge image on said target until as a signal electric current it may be converted into an output signal.

2. The pickup storage tube as claimed in claim 1 wherein there is provided an intensifying target between said photocathode and the collector mesh elecf trode, said intensifying target comprising a transparent plane member, a fluorescent membrane coated on said photocathode side of the plane member, and a second photocathode provided at the collector mesh electrode side of the plane member Ibetween the photocathode and the collector mesh electrode, thereby intensifying photoelectrons emitted from said photocathode and emitting said last mentioned photoelectrons to the collector mesh electrode side.

3. The pickup storage tube as claimed in claim 1 wherein there is provided a fluorescent membrane layer induced to emit light Ibetween said face plate and said photocathode, whereby X-ray images focused on the fluorescent membrane are stored so as to store the charge images on the target.

References Cited by the Examiner UNITED STATES PATENTS 2,700,116 1/1955 Sheldon 313-65 2,755,408 7/1956 Theile 315-11 2,776,371 1/1957 Clogston Z50-27 2,960,617 11/1960 Lodge 313-89 3,002,124 9/1961 Schneeberger 315-12 3,243,643 3/1966 Toohig 315-12 OTHER REFERENCES Knoll and Kazan, Storage Tubes, N.Y.,I John Wiley and Sons, Inc., 1952, page 119.

DAVID G. REDINBAUGH, Primary Examiner.

T. A. GALLAGHER, Assistant Examiner. 

1. A PICKUP STORAGE TUBE ADAPTED FOR STORING AN OPTICAL IMAGE AS A CHARGE IMAGE FOR A DESIRED PERIOD OF TIME COMPRISING A VACUUM ENVELOPE HAVING A FACE PLATE AT ONE END THEREOF, A PHOTOCATHODE DEPOSITED ON THE INSIDE OF SAID FACE PLATE AND ADAPTED TO EMIT PHOTOELECTRONS IN ACCORDANCE WITH THE BRIGHTNESS OF THE OPTICAL IMAGE FOCUSED ON SAID PHOTOCATHODE, A STORAGE TARGET SPACEDLY POSITIONED FROM SAID PHOTOCATHODE OPPOSITELY FROM SAID FACE PLATE, SAID STORAGE TARGET INCLUDING A METALLIC STORAGE MESH HAVING OPENINGS THERETHROUGH, AN INSULATOR COATING ON SAID MESH ON THE SIDE FACING SAID PHOTOCATHODE WHEREBY SECONDARY ELECTRONS ARE EMITTED AFTER SAID INSULATOR COATING IS STRUCK BY SAID PHOTOELECTRONS AND CHARGE IMAGES ARE STORED ON THE SURFACE OF SAID INSULATOR COATING, AND A CONDUCTIVE MATERIAL COATING ON SAID MESH ON THE OPPOSITE SIDE FROM SAID INSULATOR COATING, A COLLECTOR MESH ELECTRODE LOCATED ADJACENT AND PARALLEL TO SAID TARGET ON THE SIDE WITH SAID PHOTOCATHODE ADAPTED TO COLLECT EMITTED SECONDARY ELECTRONS, 